Most automobiles, trucks and other motor vehicles are affected by changing temperatures. For example, many internal combustion engines are more difficult to start in cold temperatures than in warm temperatures, so many modern vehicle fuel control systems adjust the start-up crank or crank-run transition fueling during cold weather to make the engine more likely to start. Accordingly, most vehicles now include an engine coolant temperature (ECT) sensor that monitors the temperature of the engine coolant during startup and operation of the vehicle. Temperature information from the ECT can be provided to a powertrain control module (PCM), engine control unit (ECU) or other controller to adjust various engine parameters to optimize performance across a wide range of operating temperatures. Similarly, ECT data may be used for diagnostic monitoring, activating various engine functions (e.g. an exhaust gas recirculation (EGR) valve or torque converter clutch) at desired temperatures, adjusting transmission shift points, varying spark advance or idle speeds, and/or many other functions.
Because vehicle exhaust generates a large percentage of air pollutants, particularly in major cities, several state, municipal and federal government agencies regulate the emissions produced by certain vehicles. The United States Environmental Protection Agency (EPA) and the California Air Reduction Board (CARB) are examples of government agencies currently regulating vehicle emissions. The On Board Diagnostic (OBD2) regulations promulgated by the EPA, for example, not only limit the amount of emissions legally produced by a vehicle, but also require that each vehicle monitor the emissions produced and issue a notification to the driver if emissions exceed a specified threshold. Because the ECT is used to adjust various engine operating parameters (e.g. fuel mixture), faults in the ECT sensor may be related to production of excess pollutants in vehicle exhaust. OBD2 and other regulations therefore require that vehicles detect sensor faults, including faults in the ECT sensor.
In particular, the OBD2 regulations require that the vehicle identify any upward bias of the ECT sensor. Monitoring the performance of the ECT sensor may be complicated, however, by the presence of an engine block heater or similar device. Because the block heater warms the engine coolant while the engine is not running, it can be difficult for the engine controller to differentiate between actual temperature increases created by the block heater and false increases created by a sensor fault.
Accordingly, it is desirable to formulate a technique for identifying irrational ECT sensor data even if an engine block heater is present in the vehicle. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.